A student examines four animals. Animal P has a solid, double nerve cord along its belly.
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A student examines four animals. Animal P has a solid, double nerve cord along its belly. Animal Q is a small sea creature with a notochord from head to tail as an adult. Animal R is a sea squirt larva with a notochord in its tail. Animal S is a frog. Which of them are chordates, and which subphylum does each chordate belong to?
Need a reminder? The key ideaShow
A chordate has a notochord, a dorsal hollow nerve cord, paired pharyngeal gill slits and a post-anal tail at some stage. Urochordata keep the notochord only in the larval tail, Cephalochordata keep it from head to tail for life, and Vertebrata replace it with a vertebral column. Non-chordates have a ventral, solid, double nerve cord and no notochord.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. Animal P. A ventral, solid, double nerve cord is a non-chordate feature. P is not a chordate; it could be an earthworm or an insect.
Step 2. Animal Q. A notochord from head to tail in the adult marks Cephalochordata, like Branchiostoma.
Step 3. Animal R. A notochord only in the larval tail marks Urochordata.
Step 4. Animal S. A frog has a vertebral column in the adult: Vertebrata.
Answer: Q, R and S are chordates: Q is a cephalochordate, R a urochordate and S a vertebrate. P is a non-chordate.
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